HYDRAULIC DRIVE CIRCUIT
WITH PARALLEL ARCHI C I ED ACCUMULATOR
Cross Reference to Related Applications
This application is being filed on 14 October 201 1, as a PCT
International Patent application in the name of Eaton Corporation, a U.S. national
corporation, applicant for the designation of all countries except the U.S., and,
QingHui Yuan, a citizen of China, applicant for the designation of the U.S. only, and
claims priority to U.S. Patent Application Serial No. 61/393,968 filed on 18 October
2010, the disclosure of which is incorporated herein by reference in its entirety.
Technical Field
The present disclosure relates generally to hydraulic drive circuits.
More particularly, present disclosure relates to hydraulic drive circuits including
accumulators for improving energy efficiency.
Background
Hydraulically powered machines employing repeating work cycles
are common in manufacturing and heavy industry. Within the work cycles of such
machines, it is common for the power demand to vary dramatically. Such power
variations can present difficulties for designing efficient hydraulic drive systems.
Low cost, energy efficient solutions are needed in this area.
FIG. 1 shows a prior art hydraulic system 8 including a hydraulic
drive circuit 20 for powering operation of a machine 19 having a repeating work
cycle (e.g., an injection molding machine). The machine 19 includes actuators 22a,
22b, 22c that are powered by the hydraulic drive circuit 20. The hydraulic drive
circuit 20 includes a fixed displacement pump 24 driven by a constant speed electric
motor 26. The pump 24 includes an inlet 28 and outlet 30. The inlet 28 connects to
a reservoir 32 (i.e., a tank) and the outlet 30 connects to a relief valve 34 and flow
control valve 36. The relief valve 34 controls the pump outlet pressure (i.e., the
hydraulic system pressure) by passing extra flow to the reservoir 32. The flow
control valve 36 controls the flow rate of the hydraulic fluid provided to the
actuators. Valves 38a, 38b and 38c are used to selectively enable and disable the
actuators 22a, 22b and 22c at different phases of the work cycle of the machine.
During operation of the system, the hydraulic system pressure is controlled via the
relief valve 34 to track the load pressure. The hydraulic system pressure typically
exceeds the load pressure by a pressure margin that corresponds generally to a
pressure drop across the flow control valve 36.
FIG. 2 depicts a system pressure profile 42 and a load pressure profile
44 for the hydraulic system 18. The system pressure profile 42 represents the
hydraulic pressure at the pump outlet over the work cycle. The load pressure profile
44 represents the hydraulic pressure demand required by the load over the work
cycle. As shown at FIG. 2, the system pressure profile 42 and the load pressure
profile 44 track one another over the entire work cycle. The system pressure profile
42 and the load pressure profile 44 are separated by a margin 46 that corresponds to
a pressure drop across the flow control valve 36. The system pressure is higher than
the load pressure throughout the work cycle.
FIG. 3 depicts a system flow rate profile 48 and a flow demand
profile 50 for the hydraulic system 18. The system flow rate profile 48 represents
the hydraulic fluid output from the pump 24 over the work cycle. The flow demand
profile 50 represents the flow required by the load over the work cycle. Since the
pump is a fixed displacement pump driven by a constant speed motor, the system
flow profile 48 is horizontal, thereby representing a constant flow output by the
pump 24 over the duration of the work cycle. The electric motor 26 and the pump
24 need to be sized to meet peak power and peak flow demands. Therefore, a
significant portion of the flow output from the pump 24 is passed to the reservoir 32
through the relief valve 34 without doing any useful work over the course of the full
work cycle. If the peak power accounts for a small percentage of the overall work
cycle, then a significant amount of energy is unused.
FIG. 4 illustrates hydraulic system 118 that uses another type of prior
art hydraulic drive circuit 120 to drive an industrial machine having a repeating
work cycle. The hydraulic drive circuit 120 has the same basic configuration as the
hydraulic drive circuit 20 of FIG. 1, except for the addition of a hydraulic
accumulator 60 and one-way check valve 62. The hydraulic accumulator 60 is
connected between the pump 24 and the flow control valve 36. The one-way check
valve 62 is installed between the accumulator 60 and the pump 24. The one-way
check valve 62 prevents back-flow from the accumulator 60 toward the pump 24.
Incorporating the accumulator 60 at the outlet side of the pump 24 filters pressure
ripple and allows the pump 24 to be downsized. By including the accumulator 60,
the pump 24 can be sized to provide the average flow required by the load over the
work cycle.
FIG. 5 depicts a load pressure profile 64, an accumulator pressure
profile 66 and a system pressure profile 68 for the work cycle of the hydraulic
system 118. As shown in FIG. 5, the pump pressure (i.e., the system pressure) is
maintained above the accumulator pressure throughout the entire work cycle. Also,
the accumulator and pump pressure track one another throughout the work cycle
Referring to FIG. 6, a pump flow profile 70, an accumulator profile
72, a load flow profile 74 and a total flow profile 76 are depicted for the work cycle
of the hydraulic system 118. The total flow profile 76 depicts the total flow
provided by the combination of the pump 24 and the hydraulic accumulator 60.
Since the pump 24 is a fixed displacement pump powered by a constant speed
electric motor 26, the flow is constant thereby causing the pump flow profile 70 to
be a horizontal line. The total flow profile 76 and the load profile 74 track one
another. When the load flow demand is less than the pump flow, excess flow from
the pump can be used to charge the accumulator 60. In contrast, when the load flow
demand is greater than the pump flow, hydraulic fluid is discharged from the
accumulator 60 so that the combined flow of the accumulator 60 and the pump 24
satisfies the load flow demand.
As shown at FIG. 6, the work cycle can be divided into alternating
charge and discharge phases. For example, the work cycle has four charge phases
(CI, C2, C3 and C4) and four discharge phases (Dl, D2, D3 and D4). The system
pressure is maintained higher than the accumulator pressure throughout the work
cycle. Also, since the accumulator is positioned on the upstream side of the
proportional valve, the flow from the accumulator has to pass through the
proportional valve to reach the load. Under conditions where the load pressure is
substantially lower than the system and accumulator pressures, significant throttling
loss can be generated across the flow control valve 36.
Summary
One aspect of the present disclosure relates to hydraulic circuit
architectures adapted to improve performance efficiency for drive circuits used to
drive loads corresponding to repetitive industrial processes.
Another aspect of the present disclosure relates to hydraulic circuit
architectures adapted for reducing throttling loss. In certain embodiments, aspects
of the present disclosure can be employed in hydraulic circuits used to drive
components of a machine or system having a repeating work cycle.
Still another aspect of the present disclosure relates to hydraulic
circuit architecture for use in a drive circuit having a hydraulic pump for driving a
load. The hydraulic circuit architecture includes a flow control valve for controlling
a hydraulic fluid flow rate supplied from the hydraulic pump to the load. The
hydraulic circuit architecture also includes a hydraulic fluid accumulator arranged in
parallel with respect to the flow control valve.
A variety of additional aspects will be set forth in the description that
follows. The aspects can relate to individual features and to combinations of
features. It should be understood that both the foregoing general description and the
following detailed description are exemplary and explanatory only and are not
restricted of the broad concepts upon which the embodiments disclosed herein are
based.
Brief Description of the Drawings
FIGURE 1 is a schematic diagram showing a prior art hydraulic
system that includes a hydraulic drive circuit that drives components of an industrial
machine;
FIGURE 2 is a graph showing hydraulic pressure profiles for one
work cycle of the system of FIG. 1;
FIGURE 3 is a graph showing flow rate profiles for one work cycle
of the system of FIG. 1;
FIGURE 4 is a schematic diagram showing another prior art
hydraulic system including a hydraulic drive circuit that drives components of an
industrial machine;
FIGURE 5 is a graph showing hydraulic pressure profiles for one
work cycle of the system of FIG. 4;
FIGURE 6 is a graph showing hydraulic flow rate profiles for one
work cycle of the system of FIG. 4;
FIGURE 7 is a schematic diagram of a hydraulic system in
accordance with the principles of the present disclosure, the hydraulic system
includes a hydraulic drive circuit for driving hydraulic components of a machine
having a repeating work cycle;
FIGURE 8 is a graph showing hydraulic pressure profiles for one
work cycle of the system of FIG. 7;
FIGURE 9 is a graph showing flow rate profiles for one work cycle
of the work cycle of the system of FIG. 7;
FIGURE 10 is a schematic diagram of another hydraulic system in
accordance with the principles of the present disclosure, the hydraulic system
includes a hydraulic drive circuit for driving hydraulic components of a machine
having a repeating work cycle;
FIGURE 11 is a graph showing hydraulic pressure profiles for one
work cycle of the system of FIG. 10; and
FIGURE 12 is a graph showing flow rate profiles for one work cycle
of the work cycle of the system of FIG. 10.
Detailed Description
FIG. 7 shows a hydraulic system 300 in accordance with the
principles of the present disclosure. The hydraulic system 300 includes a hydraulic
drive circuit 302 configured for driving a load 304 corresponding to hydraulically
driven components of a machine 303 (e.g., an injection molding machine). In the
depicted embodiment, the load 304 corresponds to a plurality of hydraulic actuators
306a, 306b and 306c that drive components of the hydraulically powered machine
303. In the depicted embodiment, the hydraulic actuator 306a is a hydraulic cylinder
powering a clamp, the hydraulic actuator 306b is a hydraulic cylinder for axially
moving an auger back and forth within a bore, and the hydraulic actuator 306c is a
hydraulic motor for the turning the auger within the bore. While the machine 303 is
depicted as an injection molding machine, it will be appreciated that aspects of the
present disclosure are applicable to any type of hydraulic powered machine. In .
particular, aspects of the present disclosure are suited for hydraulic machines having
repeating work cycles where the hydraulic pressure load and hydraulic flow load
demanded by the machines over the work cycles vary according to predefined
profiles.
The hydraulic system 300 also includes a valve arrangement 307 for
distributing hydraulic fluid flow from the drive circuit 302 to the components of the
machine 303 in a controlled manner. For example, the valve arrangement 307
enables and disables the components over the course of the work cycle so as to
implement actions of a repetitive industrial process. In the depicted embodiment,
the valve arrangement 307 includes two three-position directional control valves
308, 310 and a two position valve 312. Flow to the hydraulic actuators 306a and
306b is respectively controlled by the valves 308, 310. The valve 312 is used to
open and close fluid communication with the actuator 306c. The valves 308, 310
and 312 function as a valve arrangement for electively enabling and disabling the
actuators 306a, 306b and 306c over the course of the work cycle. Thus, the flow and
pressure demands of the load vary over the course of the work cycle depending upon
which of the hydraulic actuators 306a, 306b and 306c is enabled or disabled at a
given time during the work cycle.
While various details have been provided about the machine 303 and
the valve arrangement 307, it will be appreciated that such detail has been described
merely to provide a representative environment to which aspects of the present
disclosure can be applied. It will be appreciated that the various aspects of the
present disclosure can be used to drive machines/loads having other types of
hydraulic actuators, different configurations of actuators, and different types of
valve configurations used to enable and disable such actuators.
The hydraulic drive circuit 302 has an architecture that enables power
generation and power consumption to be effectively matched, thereby reducing
throttling power losses. Referring to FIG. 7, the hydraulic drive circuit 302 of the
hydraulic system 300 includes a circuit architecture having a hydraulic pump 314
that pumps hydraulic fluid through a work flow path 316 to the load 304. A flow
control valve 318 is provided along the work flow path 316 for controlling a
hydraulic fluid flow rate supplied from the hydraulic pump 314 to the load 304. The
hydraulic circuit architecture also includes an accumulator 320 fluidly connected to
the work flow path 316 and positioned in parallel with respect to the flow control
valve 318. The parallel configuration of the accumulator 320 assists in enhancing
the overall energy efficiency of the hydraulic drive circuit 302 over the course of a
given work cycle of the load 304. In certain embodiments, a pressure relief valve
322 is provided for controlling an outlet pressure (e.g., a system pressure) of the
pump 314.
In one embodiment, the pump 314 is a fixed displacement pump
driven by a constant speed electric motor 324. In this embodiment, the pump 314
outputs hydraulic fluid at a constant rate throughout the work cycle. The pump 314
includes an inlet 326 in fluid communication with a reservoir 328 and an outlet 330
in fluid communication with the work flow path 316. Flow output from the pump
314 in excess of the flow requirement of the load 304 is either dumped to reservoir
through the pressure relief valve 322 or used to charge the accumulator 320.
In other embodiments, however, the pump 314 may include a fixed
displacement pump driven by a variable speed electric motor (e.g., a variable
frequency drive). In still other embodiments, the pump 314 may include a variable
displacement pump. For example, disclosure of one example drive circuit having
variable pump arrangements and an accumulator may be found in copending U.S.
Application No. , filed herewith, and titled "Hybrid Hydraulic Systems for
Industrial Processes," which claims the benefit of U.S. Provisional Application No.
61/393,556, filed October 15, 2010, and titled "Hybrid System for High Efficiency
Industrial Processes," the disclosures of both of which are hereby incorporated by
reference herein.
In certain embodiments, the pressure relief valve 322 is a
proportional relief valve that can be solenoid driven. The pressure relief valve 322
includes an inlet 332 and an outlet 334. The inlet 332 is in fluid communication
with the work flow path 316 and the outlet 330 is in fluid communication with the
reservoir 328. For example, flow line 335 fluidly connects the inlet 332 to the flow
path 316 at a location between the outlet 330 of the pump 314 and the flow control
valve 318. Also, a flow line 337 fluidly connects the outlet 330 of the pressure relief
valve 322 to the reservoir 328. The pressure relief valve 322 prevents the pressure
output from the pump from exceeding a threshold level set by the pressure relief
valve. An electronic controller (e.g., electronic controller 450 described below) can
be used to adjust the threshold level of the pressure relief valve 322 over the course
of the work cycle of the machine 303.
In one embodiment, a flow control valve 318 can include a
proportional valve including a spool driven by a solenoid. The flow control valve
318 can include an inlet 338 and an outlet 340. The flow control valve 318 is
positioned downstream from the pressure relief valve 322 and the work flow path
316 passes through the flow control valve 318. An electronic controller (e.g.,
electronic controller 450 described below) can be used to control the flow control
valve 318 such that the rate of flow passing through the valve 318 equals the load
flow demand minus the accumulator discharge flow. In cases where the
accumulator is not discharging, the valve is controlled such that he flow passing
through the valve 3 8 equals the load flow demand.
In certain embodiments, the accumulator 320 is part of an
accumulator subsystem 350 that is in fluid communication with the work flow path
316. The accumulator subsystem 350 includes a charge line 352 for charging the
hydraulic fluid accumulator 320 and a discharge line 354 for discharging the
hydraulic fluid accumulator 320. The charge line 352 connects to the work flow
path 316 at a location upstream from the flow control valve 318 and the discharge
line 354 connects to the work flow path 316 at a location downstream from the flow
control valve 318.
The accumulator subsystem 350 also includes various valve
components (e.g., a valve arrangement) for controlling hydraulic fluid flow through
the subsystem. For example, the accumulator subsystem 350 includes a charge line
valve 356 for selectively opening and closing the charge line 352. The accumulator
subsystem 350 also includes a charge line one-way check valve 358 that allows
hydraulic fluid to flow through the charge line 352 from the work flow path 318 to
the accumulator 320 and prevents hydraulic fluid from flowing through the charge
line 352 from the accumulator 320 to the work flow path 318. The accumulator
subsystem 350 further includes a discharge line valve 360 and a discharge line one¬
way check valve of 362. The discharge line valve 360 is configured for selectively
opening and closing the discharge line 354. The discharge line one-way check valve
362 is configured for allowing hydraulic fluid flow to flow through the discharge
line 354 from the accumulator 320 to the work flow path 318 and to prevent
hydraulic fluid from flowing through the discharge line 354 from the work flow path
3 18 to the accumulator 320. The accumulator subsystem 350 further includes an
accumulator flow control valve 364 for controlling a charge rate of the accumulator
320 and for controlling a discharge rate of the accumulator 320.
In certain embodiments, the charge line valve 356 and the discharge
line valve 360 are two position valves each including an open position and a closed
position. The valves can include solenoid actuated spools. Additionally, in certain
embodiments, the accumulator flow control valve 364 can be a proportional valve or
variable orifice. Such a valve can include a spool the position of which is controlled
by a solenoid. In other embodiments, the valves 356, 360 can be two-position
proportional flow valves each having an open position having a variable orifice size
for proportioning flow and a closed position. This type of configuration would
eliminate the need for the accumulator flow control valve 364 since the valves 356,
360 would provide the flow proportioning function.
Referring to FIGURE 7, the flow control valve 318 can be positioned
within a valve housing 400 defining a portion of the work flow path 316. The valve
housing 400 can include an inlet port 402 that fluidly connects to the outlet 330 of
the pump 314 and an outlet port 404 that fluidly connects to the load 304.
Additionally, the housing 400 can include an accumulator charge port 406 and an
accumulator discharge port 408.
The accumulator subsystem 350 can mounted within an accumulator
housing 420. The accumulator housing can define an accumulator charge port 422
that connects with the accumulator charge port 406 of the valve housing 400 and an
accumulator discharge port 424 that connects with the accumulator discharge port
408 of the valve housing.
The hydraulic system 300 can also include an electronic controller
450 for coordinating the operation of the flow control valve 318, the accumulator
subassembly 350, the pressure relief valve 322, the directional control valve 308, the
directional control valve 310 and the two-position valve 312. Each of the aboveidentified
valves can include a spool or other structure that is actuated by a solenoid.
The electronic controller 450 can monitor the position of each spool and selectively
energizer or de-energizes the solenoids to move the valves to the appropriate
positions corresponding to a particular stage/phase in the work cycle of the machine.
Various sensors may be provided throughout the hydraulic system 300. The sensors
can interface with the electronic controller 450. Example sensors include an
accumulator pressure sensor 452, a charge port pressure sensor 454, a discharge port
pressure sensor 456, and various spool position sensors corresponding to each of the
valves. The electronic controller 450 also monitors and controls the position of the
accumulator flow control valve 364 as well as the positions of the charge line valve
356 and the discharge line valve 360. The electronic controller 450 is programmed
to control operation of the hydraulic system 300 to achieve the required load flow
and load pressure by using the minimal energy.
To design the hydraulic system, the flow and pressure demand
profiles for the work cycle of the machine 303 are determined. Flow and pressure
profiles for the accumulator and the pump are then designed to satisfy the flow and
pressure demand profiles and the pump and accumulator are sized accordingly. The
flow and pressure profiles are saved in memory and accessed by the electronic
controller 450 such that the electronic controller 450 uses the flow and pressure
profiles of the pump and the accumulator to operate the drive circuit so that the load
is provided with flow and pressure the matches the flow and pressure demand
profiles of the machine over the work cycle.
FIGURE 8 is graph showing pressure profiles for one work cycle of
the machine of FIG. 7. The pressure profile lines include a pump pressure line 470,
a load pressure line 472, and an accumulator pressure line 474. The pump pressure
and the accumulator pressures are both higher than the load pressure throughout the
work cycle. The configuration of the accumulator subsystem 350 allows the system
pressure to be set at a lower pressure than the accumulator pressure at predetermined
phases during the work cycle. This allows the system pressure to more closely
match the load pressure to enhance operating efficiency (e.g., by reducing throttling
losses).
FIGURE 9 is a graph showing flow rate profiles for the machine of
FIG. 7. The flow rate profiles include a load demand flow 480, a total flow 482, a
pump flow 484, and an accumulator flow 486. Total flow 482 is the total of the
pump flow 484 and the accumulator flow 486. As shown in FIG. 9, the pump flow
has a constant flow rate throughout the duration of the work cycle of the machine.
Also, the total flow matches the load flow and the accumulator flow tracks/parallels
the load flow.
When the flow demand of the load is less than the pump flow rate,
the electronic controller 450 opens the charge line 352 and closes the discharge line
354 such that the accumulator 320 is charged. Thus, the system operates in a charge
mode or phase. In the charge phase, the electronic controller 450 sets the system
pressure to be either the accumulator pressure demand or the load pressure,
whichever is higher, plus a margin. During charging, electronic controller controls
the accumulator flow control valve 364 to achieve a desired charge flow to the
accumulator.
When the flow demand of the load is greater than the flow rate of the
pump, the electronic controller 450 closes the charge line 352 and opens the
discharge line 354 such that the pump and the accumulator cooperate to satisfy the
flow demand of the load. Thus, the system operates in a discharge mode or phase.
In the discharge phase, the electronic controller 450 sets the system pressure to be
the load pressure plus a margin if the accumulator alone can not satisfy the load flow
demand. Alternatively, if the accumulator flow alone can satisfy the load flow
demand, the system pressure is set to a minimal pressure. During accumulator
discharge, electronic controller controls the accumulator flow control valve 364 to
achieve a desired discharge flow from the accumulator.
As shown at FIGURES 8 and 9, the hydraulic system 300 has four
charge phases (CI, C2, C3 and C4) and four discharge phases (Dl, D2, D3 and D4)
over the course of one work cycle. The electronic controller 450 controls the
various valves of the system to achieve the pressure and flow profiles of FIGURES
8 and 9 for each cycle.
A hydraulic accumulator operates most efficiently when sized such
that the accumulator pressure fairly closely matches the pressure of the load. This
can present a difficulty when the accumulator is used to drive a load having a work
cycle with a wide range of pressures. Specifically, in industrial processes where the
load pressure varies dramatically, the mismatch between accumulator pressure and
the load pressure can cause significant throttling loss. To address this situation,
another aspect of the present disclosure relates to using an accumulator array (i.e.,
multiple accumulators) to improve the overall operating efficiency of a hydraulic
drive circuit. Each accumulator of the array is configured or designed to operate at a
different working pressure range. For example, one accumulator operates in a high
pressure range, while another accumulator operates in a low pressure range. During
the course of a given work cycle, the high pressure and low pressure accumulators
will be selectively activated and deactivated to match the pressure of the load. For
example, when the load is at a phase of the work cycle that requires low pressure
flow, the low pressure accumulator can be activated and the high pressure
accumulator can be deactivated. In contrast, when the load is at a phase of the work
cycle that requires high pressure flow, the high pressure accumulator can be
activated and the low pressure accumulator can be deactivated. During other parts
of the work cycle, both accumulators may be deactivated. It will be appreciated that
by using more than two accumulators in the array, the hydraulic drive circuit can be
more finely tuned to match the load pressures corresponding to different
times/phases in the work cycle.
FIG. 10 depicts another hydraulic system 500 in accordance with the
principles of the present disclosure. The hydraulic system 500 modifies the parallel
accumulator architecture of the hydraulic system 300 of FIG. 7 to include an
accumulator array as compared to a single accumulator. The basic components of
the hydraulic system 500 are the same as those described with respect to the
hydraulic system of FIG. 7 and therefore have been assigned like reference numbers.
The design has been modified to include first and second accumulator subsystems
350a, 350b that are both arranged in parallel with respect to the flow control valve
318. The accumulator subsystems 350a, 350b have the same configuration as the
subsystem 350. However, the accumulator subsystem 350a has an accumulator 320a
having a different accumulator pressure operating range than an accumulator 320b
of the accumulator subsystem 350b. In one embodiment, the accumulator 320a has
a higher accumulator pressure operating range than the accumulator operating range
of the accumulator 320b. In one embodiment, the accumulator 320a is a high
pressure accumulator and the accumulator 320b is a low pressure accumulator.
An electronic controller and various sensors are not shown in FIG 10.
However, it will be appreciated that such an electronic controller can be used as
described above to control the various components in accordance with pre-defined
pressure and flow profiles so as to match the flow and pressure demands of the load
over the work cycle. The components can be controlled (e.g., selectively activated
and de-activated) based on the predetermined timing and sequencing defined by the
pre-defined flow and pressure profiles, or can be controlled on a real-time basis
based on sensed pressure and flow rate data.
In operation of the system, the electronic controller controls charge
and discharge of the accumulators 320a, 320b. Preferably, when one of the
accumulators 320a, 320b is charging or discharging, the other of the accumulators is
inactive. For example, during a phase of the work cycle where the demand flow is
higher than the pump flow and the load pressure is relatively high, the high pressure
accumulator 320a can be discharged to assist the pump in satisfying the flow
demanded by the load. During discharge of the high pressure accumulator 320a, the
low pressure accumulator 320b is inactive. During a phase of the work cycle where
the demand flow is higher than the pump flow and the load pressure is relatively
low, the low pressure accumulator 320b can be discharged to assist the pump in
satisfying the flow demanded by the load. During discharge of the low pressure
accumulator 320b, the low pressure accumulator 320b is inactive. The accumulators
320a, 320b can be charged during phases of the work cycle where the load flow
demand is less than the pump/system flow.
FIGURE 1 is graph showing pressure profile lines for the hydraulic
system 500 of FIG. 10 over an example work cycle. Accumulator and pump
pressure profile lines corresponding to the drive system of the hydraulic system 500
are configured to match an example load pressure demand profile line 502. The
accumulator and pump profile lines include an accumulator pressure profile line 504
corresponding to the accumulator 320a, and accumulator pressure profile line 506
corresponding to the accumulator 520b, and a pump pressure profile line 508
corresponding to the system pressure produced by the pump 314.
FIGURE 12 is graph showing flow rate profile lines for the hydraulic
system 500 of FIG. 10 over an example work cycle. Accumulator and pump flow
profile lines corresponding to the drive system of the hydraulic system 500 are
configured to match an example load flow demand profile line 510. The flow rate
profile lines for the hydraulic drive of the hydraulic system 500 include an
accumulator flow profile 512 corresponding to the accumulator 320a, an
accumulator flow profile 514 corresponding to the accumulator 320b and a pump
flow profile 516 corresponding to the pump 314. Figure 12 also shows that the total
flow, which represents the combined flow provided by the pump 314 and the
accumulators 320a, 320b over the duration of the work cycle closely tracks the load
flow profile and is shown as the same line as the load flow profile. In practice, the
total flow can be slightly larger than the load flow.
Referring to Figures 11 and 12, over the course of the work cycle the
hydraulic system 500 has at least charge phases C1-C4 and at least discharge phases
D1-D4. The low pressure accumulator 320b is charged and discharged at phases CI
and Dl. The high pressure accumulator 320a is charged and discharged at the
remainder of the charge and discharge phases. At the charge phase CI and
discharge phase Dl, the pressure demanded by the load is relatively low. By using
the low pressure accumulator 320b in these phases, it is possible to significantly
lower the operating pressure of the pump 314 to more closely match the pressure
demand of the load (see region 515). This can provide energy savings relating to
reduced throttling losses. Energy savings can also be provided at each of the
discharge phases because the parallel arrangement of the accumulators allows the
system pressure to be lower to be more closely match the load pressure demand (see
regions 517). In Figure 12, box 520 represents the portion of the work cycle where
the high pressure accumulator 320a is active and the low pressure pump 320b is
deactivated. Also, box 522 represents the portion of the work cycle where the low
pressure accumulator 320b is active and the high pressure accumulator 320a is
deactivated.
To design the hydraulic system 500 of FIG. 10, the force and speed
requirements for the work cycle of the machine 303 are acquired. Next, force and
speed requirements are converted into pressure and flow demand profiles for the
work cycle (e.g., profile lines 502 and 510). Based on the flow profile and minimum
pump flow, the charge and discharge phases for the accumulators of the accumulator
array are established. Once the charge and discharge phases have been established,
the pressure profile demand for the work cycle is evaluated and used to assign the
appropriate accumulator to the appropriate charge and discharge phase based on how
closely the operating pressure ranges of the accumulators match the load pressure
demand during the phase. The actual charge and discharge flow of each
accumulator is configured such that the state of charge for a given accumulator at
the end of the cycle is identical to that in the beginning. Also, the flow of the system
over the work cycle is assessed such that the summation of the pump flow and the
accumulator flow is always greater than the load flow. In designing the system, it is
preferably assumed that there is a gap in time from work cycle to work cycle. Such
a gap in time can be leveraged to charge or discharge the accumulators as needed. If
no gap in time exists between the two work cycles, the flow within each phase may
be adjusted and the pump flow requirement maybe increased accordingly.
Once the overall flow strategy and flow and pressure profiles have
been established, the accumulator sizes and pressure ranges can be determined.
Also, the necessary precharge values for the accumulators are calculated.
Preferably, during discharge, the accumulator pressures should be higher than the
load pressures. The pump and electric motor can be sized/configured based on the
determined flow and pressure profiles.
When one of the accumulators is in charge mode, the system is set to
the larger of the accumulator pressure or the load pressure plus a marginal pressure,
the charge path to the accumulator is opened, and the flow control valve 318 is
controlled to meet the flow demand. In the charge mode, the flow rate control valve
318 is controlled such that the flow passing through the valve 318 equals the flow
demand of the load taking into consideration the rate of flow being directed into the
accumulator through the charge path and the accumulator flow control valve 364.
When one of the accumulators is in the discharge mode, the system pressure is set to
load pressure plus a marginal pressure, the flow control valve 318 is fully opened
and the accumulator flow control valve 364 is controlled such that the discharge
flow rate combined with the flow rate to valve 18 equals the load flow rate
demand.
It will be appreciated that the various graphs and data presented
herein are the product of computer simulation not empirical data. Such information
is provided to illustrate certain general concepts and operating modes of systems in
accordance with the principles of the present disclosure and is not intended to be
relied upon as precise empirical data.
Various modifications and alterations of this disclosure will become
apparent to those skilled in the art without departing from the scope and spirit of this
disclosure, and it should be understood that the scope of this disclosure is not to be
unduly limited to the illustrative embodiments set forth herein.
CLAIMS:
1. A hydraulic circuit architecture for use in a drive circuit having a hydraulic
pump for driving a load, the hydraulic circuit architecture comprising:
a flow control valve for controlling a hydraulic fluid flow rate
supplied from the hydraulic pump to the load; and
a hydraulic fluid accumulator arranged in parallel with respect to the
flow control valve.
2. The hydraulic circuit architecture of claim 1, wherein the flow control valve
is a proportional flow valve.
3. The hydraulic circuit architecture of claim 1, further comprising a relief
valve for controlling a hydraulic system pressure output by the pump.
4. The hydraulic circuit architecture of claim 3, wherein the relief valve is a
proportional relief valve.
5. The hydraulic circuit architecture of claim 1, wherein the hydraulic pump is a
fixed displacement pump.
6. The hydraulic circuit architecture of claim 5, further comprising a constant
speed electric motor for driving the fixed displacement pump.
7. The hydraulic circuit architecture of claim 1, further comprising a work flow
path that extends from the pump through the flow control valve to the load, wherein
the hydraulic circuit architecture includes an accumulator subsystem in fluid
communication with the work flow path, the accumulator subsystem including a
charge line for charging the hydraulic fluid accumulator and a discharge line for
discharging the hydraulic fluid accumulator, wherein the discharge line connects to
the work flow path at a location downstream from the flow control valve, and
wherein the charge line connects to the work flow path at a location upstream from
the flow control valve.
8. The hydraulic circuit architecture of claim 7, further comprising:
a charge line valve for selectively opening and closing the charge
line;
a charge line one-way check valve that allows hydraulic fluid to flow
through the charge line from the work flow path to the accumulator and
prevents hydraulic fluid from flowing through the charge line from the
accumulator to the work flow path;
a discharge line valve for selectively opening and closing the
discharge line; and
a discharge line one-way check valve that allows hydraulic fluid to
flow through the discharge line from the accumulator to the workflow path
and prevents hydraulic fluid from flowing through the discharge line from
the work flow path to the accumulator.
9. The hydraulic circuit architecture of claim 8, wherein the charge line valve
and the discharge line valve each comprise a two position valve including an open
position and a closed position.
10. The hydraulic circuit architecture of claim 8, wherein the accumulator circuit
includes an accumulator flow control valve for controlling a charge rate of the
accumulator and for controlling a discharge rate of the accumulator.
11. The hydraulic architecture of claim 6, further comprising:
a relief valve for controlling a hydraulic system pressure provided to
the flow control valve by the pump;
a first valve arrangement for enabling and disabling actuators
corresponding to the load;
a second valve arrangement for controlling charging and discharging
of the accumulator; and
an electronic controller for coordinating operation of flow control
valve, the relief valve and the first and second valve arrangements such that
the hydraulic accumulator is charged when a flow demand of the load is less
than an output flow of the hydraulic pump and the hydraulic accumulator
discharges when the flow demand of the load is greater than the output flow
of the hydraulic pump.
12. The hydraulic architecture of claim 11, wherein during discharge of the
accumulator the hydraulic system pressure is less than the accumulator pressure.
13. The hydraulic architecture of claim 1 , wherein the actuators power
components of a machine having a repeating work cycle, the work cycle including a
pressure demand having a pressure profile that varies over a plurality of phases of
the work cycle and a flow demand having a flow profile that varies over the plurality
of phases of the work cycle.
14. The hydraulic architecture of claim 13, wherein the machine comprises an
injection molding machine and the actuators include a first hydraulic cylinder
powering a clamp, and second hydraulic cylinder for axially moving an auger and a
hydraulic motor for rotating the auger.
15. The hydraulic architecture of claim 1, wherein the hydraulic fluid
accumulator is a first hydraulic fluid accumulator, wherein a second hydraulic fluid
accumulator is also arranged in parallel with respect to the flow control valve, and
wherein the first and second hydraulic fluid accumulators have different
accumulator operating pressure ranges.
16. A method for driving a load with a drive circuit having a hydraulic pump, the
drive circuit including a flow control valve for controlling a hydraulic fluid flow rate
between the hydraulic pump and the load and a hydraulic fluid accumulator arranged
in parallel with respect to the flow control valve, the load corresponding to actuators
of a machine having a repeating work cycle, the work cycle including a pressure
demand having a pressure profile that varies over a plurality of phases of the work
cycle and a flow demand having a flow profile that varies over the plurality of
phases of the work cycle, the method comprising:
using flow from the hydraulic pump to drive the load and charge the
accumulator when the flow demand of the load is less than an average system flow
for the work cycle; and
using flow from the hydraulic pump and discharge flow from the
accumulator to drive the load when the flow demand of the load is larger than the
average system flow for the work cycle, wherein during discharge of the
accumulator a hydraulic system pressure at an outlet of the hydraulic pump is
controlled such that the hydraulic system pressure is less than a hydraulic pressure of
the accumulator.
17. The method of claim 16, wherein the hydraulic fluid accumulator is a first
hydraulic fluid accumulator, wherein the drive circuit includes a second hydraulic
fluid accumulator arranged in parallel with respect to the flow control valve, wherein
the first hydraulic fluid accumulator has a higher accumulator operating pressure
range than an accumulator operating pressure of the second hydraulic fluid
accumulator, and wherein one of the first and second hydraulic fluid accumulators is
selected to provide the discharge flow based on how closely the accumulator
operating pressure matches a demand pressure of the load.
18. A hydraulic drive system for powering a load, the hydraulic drive system
comprising:
a fixed displacement hydraulic pump;
a constant speed electric motor for driving the fixed displacement
hydraulic pump;
a relief valve for controlling a system pressure of the fixed
displacement hydraulic pump;
a flow control valve for controlling a hydraulic fluid flow rate
supplied from the fixed displacement hydraulic pump to the load; and
a first hydraulic fluid accumulator arranged in parallel with respect to
the flow control valve.
19. The hydraulic drive system of claim 18, further comprising a second
hydraulic fluid accumulator arranged in parallel with respect to the flow control
valve.
20. The hydraulic drive system of claim 19, each of the first and second
hydraulic fluid accumulators includes an accumulator circuit including :
a charge line positioned upstream from the flow control valve;
a discharge line positioned downstream from the flow control valve;
a charge line valve for selectively opening and closing the charge
line; and
a discharge line valve for selectively opening and closing the
discharge line.